Why DST (Daylight Saving Time) change in the clock happened one hour later than the expected time?

Issue

• tzdata package was updated on the system to have DST followed but it did not happened at expected time, and was in the effect one hour later (at scheduled time). By default time (according to zdump) it is suppose to be at 2am. It was set to happen at 1am where it was executed at it's default time.

# DST time
/etc/localtime  Sun Mar 29 01:00:00 2015 UTC = Sun Mar 29 02:00:00 2015 BST isdst=1 gmtoff=3600